1. Field of the Invention
The present invention relates to a patch antenna device, and more particularly to a vehicle-mounted patch antenna device that can be reduced in size while performance is improved.
2. Description of the Related Art
Lately, there has been known a patch antenna as an antenna used for a vehicle-mounted device, such as what is called an electronic toll collection system (ETC). The patch antenna is also called a microstrip antenna, which has characteristics of being low in height and having a narrow bandwidth. The patch antenna has a structure in which an antenna element is disposed on a ground conductor with a substrate and an air layer provided between them.
There also exists an antenna device that includes electric circuits, such as a light-emitting diode and a speaker, incorporated in the antenna device, and has a function of notifying operation, a state, and the like of the antenna device, like antenna devices described in Patent Document 1 and Patent Document 2. In a microstrip antenna attached with a light-emitting diode disclosed in Patent Document 1, there is provided a light-emitting diode in a location in which a potential difference between an antenna element and a ground conductor is minimum when the antenna element resonates. In this manner, an area of a substrate around an outer side of the antenna element is reduced. In a speaker-integrated antenna disclosed in Patent Document 2, a piezoelectric ceramic member is adhered to a ground conductor. In this manner, the ground conductor is allowed to have a function as a speaker in pursuit of reduction in size of the antenna device. A speaker circuit is connected to a power feeding point of the antenna element.
In a vehicle-mounted patch antenna device described in Patent Document 3 filed by the same applicant as the present application, an antenna element section is provided on a surface facing a surface on which a ground conductor is provided of a substrate. A notification circuit section provided on a side of the surface on which the ground conductor is provided is connected adjacent to an area where current distribution is minimum in a peripheral area other than an area in which a power feeding section of the antenna element section is provided.